This invention relates to plasma enhanced chemical vapor deposition. More particularly, it relates to deposition in an expanding thermal plasma (hereinafter referred to as “ETP”) apparatus to coat substrates.
Yang et al. U.S. Pat. No. 6,110,544 discloses an ETP method and apparatus for depositing an adherent coating onto a surface of a substrate by plasma deposition. The process comprises passing a plasma gas through a direct current arc plasma generator to form a plasma. A substrate is positioned in an adjoining vacuum chamber. A reactant gas and an oxidant are injected into the plasma. The plasma is expanded into a diverging nozzle-injector extending from the plasma generator into the vacuum chamber towards the substrate. A reactive species formed by the plasma from the oxidant and reactant gas contact the surface of the substrate for a period of time sufficient to form an adherent coating.
Coatings that can be deposited by ETP include silicon oxide-based hardcoats that protect a plastic substrate from abrasion. Also, ETP can be used to deposit metal oxide-based coatings such as zinc oxide. High coating deposition rates can be achieved by ETP at relatively low temperatures. Hence, ETP is particularly valuable to coat lower Tg materials such as a polycarbonate (hereinafter “PC”) sheet or film. However, while current ETP apparatus and processes are valuable, it is always desirable to provide an improved deposition apparatus and method that can be controlled to produce a desired product or that can be operated at lower cost.